1. Field of the Invention
This invention relates to a wheel speed detecting device which detects the rotational speed of a wheel.
2. Description of Related Art
Motorcycles adopting, for instance, an Antilock Brake System (ABS) are equipped with a wheel speed detecting device for detecting the rotational speed of front and rear wheels. As a background art wheel speed detecting device, the xe2x80x9cWheel Speed Detecting Device in Motorcyclesxe2x80x9d disclosed in Japanese Patent Laid-Open No. H8-133154 has been known. This background art will be explained in detail by referring to FIG. 18.
FIG. 18 is a side view of a background art wheel speed detecting device. The wheel speed detecting device mounted on the rear wheel of a motorcycle will be explained below.
In a wheel speed detecting device 150, a sensor ring (hereinafter referred to as the xe2x80x9cpulsar ringxe2x80x9d) 153 is attached on a spoke portion 152 of a rear wheel 151. A pulse counting sensor 156 (e.g., an electromagnetic rotary sensor) is attached on a swing arm 155 which supports the rear wheel 151, oppositely to teeth 154 of the pulsar ring 153.
According to the wheel speed detecting device 150, with the rotation of the rear wheel 151, the pulsar ring 153 rotates together with the rear wheel 151, while the teeth 154 of the pulsar ring 153 pass the pulse counting sensor 156. The pulse counting sensor 156 counts the teeth 154 that have passed thereby, thus detecting the wheel speed of the rear wheel 151 (the rotational speed of the rear wheel 151).
To improve the detection accuracy of the teeth 154 by the pulse counting sensor 156, it is desirable to mount the pulse counting sensor 156 close to the teeth 154. In order to mount the pulse counting sensor 156 close to the teeth 154, it is necessary to set the flatness of the pulsar ring 153 (particularly, the teeth 154).
If the flatness of the pulsar ring 153 exceeds a permissible range, unevenness of the pulsar ring 153 increases. It is therefore necessary set the pulse counting sensor 156 apart from the teeth 154 with the unevenness taken into account. Accordingly, it is difficult to improve the detection accuracy of the teeth 154 by the pulse counting sensor 156.
The teeth 154 of the pulsar ring 153, therefore, have been formed by a cutting process to set the flatness of the pulsar ring 153 (especially the teeth 154 ) within the permissible range. This processing of the pulsar ring 153 requires time and labor, thus increasing the cost.
Forming the pulsar ring 153 by pressing has also been considered. However, since the teeth 154 are relatively long and slender, if processed by pressing, the teeth 154 of the pulsar ring 153 will be subjected to warpage.
Therefore, it is necessary to correct the warpage of the teeth 154 after pressing the pulsar ring 153. This also increases the time and labor, thus increasing cost.
It has therefore been desired to put into practice a wheel speed detecting device capable of enhancing the detecting accuracy and lowering cost.
It is therefore an object of the present invention to provide a device which can enhance the detecting accuracy of a wheel speed detecting device and lower the cost.
In view of the above-described problems, the wheel speed detecting device according to a first aspect of the present invention comprises a pulsar ring attached on the wheel side and a pulse counting sensor attached on the vehicle body side. The pulsar ring comprises a disc, and pulse detecting holes or pulse detecting recesses are provided at a predetermined pitch on a pitch circle drawn in a radially inward circumferential position spaced at a distance from an outer edge of the disc.
The pulse detecting holes are opened at a position on the center side, spaced from an outer edge of the pulsar ring, whereby the outer edge of the pulsar ring can remain in a circular shape. Therefore, it is possible to reduce warpage of the pulsar ring at the outer edge if the pulse detecting holes are formed by pressing. Furthermore, the flatness of the pulsar ring can be held within the permissible range.
According to a second aspect of the present invention, when the disc has a sensing surface on the side directed toward the pulse counting sensor, a stiffening rib is provided in the vicinity of, or on the back side of, the sensing surface.
The sensing surface can be increased in rigidity by providing the stiffening rib in the vicinity of, or on the back side of, the sensing surface. Therefore, if the pulsar ring has a reduced plate thickness, it is possible to ensure the flatness of the sensing surface within the permissible range, while enabling a reduction in weight of the pulsar.
A third aspect of the present invention is characterized in that the stiffening rib is provided along the sensing surface, and the height of this stiffening rib is set larger than the clearance from the sensing surface to the pulse counting sensor.
The stiffening rib is provided along the sensing surface and the height of this stiffening rib is increased larger than the clearance from the sensing surface to the pulse counting sensor. Therefore, it is possible to cover the clearance between the sensing surface and the pulse counting sensor with the stiffening rib, the stiffening rib being usable as a protective cover. Therefore, the clearance between the sensing surface and the pulse counting sensor is protected by the stiffening rib, so that the clearance can be prevented from catching a flying substance such as a flying rock.
Furthermore, since the stiffening rib is usable as a protective cover, no individual protective cover is needed, thereby preventing an increase in the number of components. Accordingly, the time and effort required to install a protective cover can be dispensed with.
In a fourth aspect of the present invention, the stiffening rib is formed by bending the outer edge of the disc.
With this construction, the wheel speed detecting device can be improved in quality by increasing the rigidity of the pulsar ring with the outer edge of the disc being bent.
Furthermore, a pulsar ring of predetermined thickness can be obtained with a decrease in weight, making it possible to decrease cost and to improve vehicle performance.
A fifth aspect of the present invention is characterized in that the pulsar ring is prepared from a pressed part with punched pulse detecting holes, and one or both sides of the pulsar ring which faces toward a punch is called the first side and the other is the second side. Furthermore, the pulsar ring is attached so that the second surface faces the pulse counting sensor.
When the pulse detecting hole is punched from the first side through to the second side, the edge of the hole in the first side becomes round, while the hole in the second side has a sharp edge.
In the fifth aspect of the present invention, the pulsar ring is attached with the second side having the sharp-edge holes directed toward the pulse counting sensor.
By using the pulsar ring having sharp-edge holes, the sensing performance of the pulse counting sensor can be improved.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.